Gold atoms can be the key to making new materials with fascinating and frequently beautiful arrangements of atoms. For example, materials made from gold, sodium and gallium contain gold atoms arranged into tetrahedra, rods of hexagonal stars, or diamond-like three-dimensional frameworks. For certain gold concentrations, gold interacts in a novel way with sodium and stabilizes the formation of icosahedra. Icosahedral atomic arrangements are seen in many quasicrystalline materials — materials that lack the periodic long-range order of conventional crystals and exhibit crystallographically-forbidden rotational symmetries — so this prompted the idea that further tuning might lead to new quasicrystalline materials, and the discovery of the world’s first sodium-containing quasicrystals. The surprising structural versatility of gold is opening up whole new insights into structure-bonding relationships involving clusters of atoms and bulk solids.
A Sodium-containing Quasicrystal: Using Gold to Enhance Sodium’s Covalency in Intermetallic Compounds